1. Technical Field
The present invention relates to packet-data communication and, more particularly, to improving the initiation of packet-data communication sessions involving mobile stations.
2. Description of Related Art
More people than ever are using mobile stations, such as cellular telephones and personal digital assistants (PDAs), to connect to radio access networks (RANs), which are also referred to as wireless networks, wireless wide area networks (WWANs), wireless communication systems, cellular communication systems, wireless access networks, and by other names. Service providers typically operate RANs to provide both voice and data services using a wireless communication format such as Code Division Multiple Access (CDMA), or another format. Relevant aspects of CDMA are described in the known industry standards IS-95 and IS-2000, which are incorporated herein by reference.
As mentioned above, mobile stations connect to RANs to engage in both voice and packet-data communication sessions. These packet-data communication sessions may take the form of, as examples, web-browsing sessions, e-mail sessions, instant-messaging sessions, Voice over Internet Protocol (VoIP) sessions, and/or any other type of packet-data communication sessions. To engage in these sessions, mobile stations may use a packet-switched protocol such as the Internet Protocol (IP), relevant aspects of which are described in “Internet Protocol,” RFC 791 (September 1981), which is incorporated herein by reference.
Certain types of packet-data communication sessions, such as VoIP sessions, may be set up using a protocol such as the Session Initiation Protocol (SIP), relevant aspects of which are described in Rosenberg et al., “SIP: Session Initiation Protocol,” RFC 3261 (June 2002), which is incorporated herein by reference. The SIP messages involved in setting up these packet-data communication sessions may include description of one or more parameters of those sessions according to a protocol known as the Session Description Protocol (SDP). These parameters may include codecs, communication protocols, and/or any other parameters. Relevant aspects of SDP are described in Handley and Jacobson, “SDP: Session Description Protocol,” RFC 2327 (April 1998), which is incorporated herein by reference.
Mobile stations implementing SIP may include a functional entity known as a SIP client, which, perhaps via a network entity known as a SIP server or SIP proxy, transmits messages to and receives messages from a SIP client in the device with which the mobile station is attempting to initiate the, for example, VoIP session. The mobile station typically sends these SIP messages to and receives these SIP messages from a SIP server communicatively connected to the RAN. Thus, the SIP messages traverse the air interface between the mobile station and the RAN.
Once the session parameters have been agreed upon by the two devices, the session may be conducted using a bearer protocol such as the Real-time Transport Protocol (RTP), relevant aspects of which are described in Schulzrinne et al., “RTP: A Transport Protocol for Real-Time Applications,” RFC 3550 (July 2003), which is incorporated herein by reference. Many other protocols may used instead of or in addition to RTP, however.
Another known example of a VoIP-call-setup sequence involves a packet-based or legacy telephone connected to an IP-telephony gateway, which engages in call-setup signaling, perhaps with another gateway, on behalf of the telephone, using a protocol such as H.323 or SIP. Also, devices known as media (or analog) terminal adapters are known to function as gateways that engage in SIP-based call-setup signaling on behalf of non-SIP devices. Finally, it is known for devices referred to as soft-switches or soft mobile switching centers (“soft MSCs”) to engage in SIP-based call-setup signaling on behalf of mobile stations.